Double insulated hand tool



Sept. 26, 1967 L. c. PRATT 3,344,291

' DOUBLE INSULATEDYHAND TOOL 7 Filed Nov. 23, 1964' 2 Sheets-Sheet L i INVENTOR. LEONARD a. PRATT QM wT-vuwr ATTORN EY Se t. 26, 1967 L c. PRATT DOUBLE INSULATED 1mm TOOL 2 Sheets-Sheet 2 Filed Nov. 23, 1964 Y I 'INVENTOR.

- LEONARD 6. PRATT ATTORNEY United States Patent Ofiice 3,344,291 Patented Sept. 26, 1967 3,344,291 DQUBLE INSULATED HAND TOGL Leonard C. Pratt, Greenfield, Mass, assignor to Millers Falls Company, Greenfield, Mass., a corporation of Massachusetts Filed Nov. 23, 1964, Ser. No. 413,272 2 Claims. (Cl. 310-50) ABSTRACT OF THE DISCLOSURE An electrically powered hand tool wherein certain portions of the housing are formed from insulating material, an insulating sleeve surrounds the field structure, and a double covering of insulating material is provided on the armature shaft.

The disclosure This invention relates to electrically powered hand tools and the like and has particular reference to the provision of new and improved double insulating means for an electrically powered hand tool.

Broadly considered, double insulation as applied to an electrically powered hand tool comprises two separate layers or coverings of electrical insulation. More specifically, double insulation for such a tool comprises a first layer or covering of functional electrical insulation adapted to provide normal insulation throughout the operation of the tool and a second layer or covering of protecting electrical insulation designed to provide adequate tool insulation should a failure or weakening occur in the functional insulation.

An object of the present invention is to provide new and improved double insulating means for an electrically powered hand tool, such as, for example, an electrically powered impact wrench.

Another object of the invention is to provide new and improved insulating means of the type set forth which is adapted to provide adequate tool insulation throughout all phases of operation of the electrically powered tool.

Another object is to provide new and improved insulating means of the type set forth which maintains the structural strength of the members forming the power tool wherever tool strength is of importance.

Another object is to provide new and improved insulating means of the type set forth which is adapted to withstand the self-destructive forces generated in the operation of a power hand tool.

Another object is to provide new and improved insulating means of the type set forth which includes means for directing the flow of air within the tool.

Another object is to provide new and improved insulating means of the type set forth which includes means constructed and arranged such as to provide double insulation for the external power leads and power switches upon the tool.

Another object is to provide new and improved insulating means of the type set forth which is both eificient in operation and economical in construction.

Other objects and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings. It will be understood that changes may be made in the details of construction and arrangement of parts shown and described as the preferred form of the invention has been given by way of illustration only.

Referring to the drawings:

FIG. 1 is an external elevational, side view of an electically powered impact wrench constructed in accordance with the present invention;

FIG. 2 is an enlarged, elevational side view, partially bro-ken away and in section, of the impact wrench shown in FIG. 1;

FIG. 3 is a rear, external view on said impact wrench;

FIG. 4 is an enlarged, sectional view of the power unit of said impact wrench in combination with insulating means provided by the present invention; and

FIG. 5 is a perspective view of a double insulating means provided by the present invention.

It will be understood that, although the followin description and the accompanying drawings describe the double insulating means provided by the present invention as applied to an electrically operated impact wrench, such has been shown for the purposes of illustration only. The spirit and scope of the present invention are not limited to impact wrenches, but rather, encompass other similarly constructed electrically powered hand tools.

Referring more particularly to the drawings wherein similar reference characters are used to designate corresponding parts throughout the several views, and with particular reference to FIGS. 1 and 3, the electrically powered hand tool illustrated therein comprises an impact wrench which is designated generally at It).

The impact wrench 10 includes a casing or housing 12 which is formed by the rear or motor housing 14, the forward housing 16, and the separator 15 which is interposed between the housings 14 and 16 and operatively joined therewith by the fastening means 17. Motor housing 14, separator 15, and forward housing 16 are constructed of a non-insulating metallic material, such as aluminum or the like, and are particularly adapted to receive the stress and other forces normally incident to the operation of the impact wrench in. An impact anvil 20 is operatively carried by impact wrench 10 adjacent the forward end of the forward housing 16.

The casing 12 further includes a back cap 22, constructed of plastic or other suitable insulating material, which is secured relative to the motor housing 14 by retaining means 24. Air intake means, such as the slots 2211, may be formed in the back cap 22 which, as will be later herein shown, forms a portion of the double insulation means provided by the present invention.

A handle 26 constructed of insulating material, such as plastic or the like, is operatively secured to the motor housing 14 adjacent the lower surface thereof. The handle 26 provides support for the impact wrench actuator or trigger 28 and serves to introduce into the impact Wrench 10 the electrical leads 36 which operatively conmeet the impact wrench 16 with an external source of electrical power. The electrical leads 30 are of conventional construction and are provided with an external covering of insulating material throughout their length.

As illustrated in FIG. 2, the electrical leads 3t) pass through an insulating sleeve 13 which is associated with the handle 26 prior to their entrance into the handle 26. Although the electrical leads 30 have been illustrated as passing into the handle 26 adjacent the upper end thereof, however, it will be understood that such has been shown for the purposes of illustration only. Alternatively, for example, the electrical leads 30 could be admitted into the handle 26 at the lower end 32 thereof.

Internally of the handle 26, the electrical leads 30 are electrically connected to the electrical switch means 34. The switch means 34 are, in turn, electrically connected through the insulated electrical leads 36 to the motor 38 of the impact Wrench 10, the leads 3d passing through the cooperating openings 40 and 42 in the handle 26 and the motor housing 14, respectively, during this connection.

The trigger 28 is operatively positioned within a slot 44 in the handle 26 and is adapted to actuate the switch means 34 to control the flow of electricity to the motor 38. The trigger 2S, furthermore, preferably is an insulated member and is constructed of plastic or other suitable insulating means.

The handle 26 includes an insulating barrier 46 which provides additional insulation between the handle 26 and the metallic motor housing 14. The side surfaces 48 of the corresponding openings 40 and 42 in the handle 26 andthe motor housing 14, respectively, are provided with an insulating sleeve 56 which affords a double insulation to the insulated leads 36 passing through said openings.

In view of the foregoing, it will be seen that the insulating handle 26 provides a double insulation for the insulated trigger 28 and the insulated electrical leads 30 and 36.

The motor 38 of the impact wrench is carried by the motor housing 14 and comprises, generally, a shaft 52 which is journalled for rotary movement in the bearings relative to the field core 62 and electrically connected by the leads 36 to the switch means 34. Functional insulation for the core 62 and coil 64 is provided by the insulating member 66 which is disposed between the core 62 and the metallic motor housing 14 and the external insulating coating which is formed upon the coil 64.

The field coil 64, furthermore, is electrically connected to the commutator brush means 68 through the electrical leads 70 which are electrically connected through connecting means such as the screw-type contact means 72, the contact plate 74 which is operatively associated with the contact means 72, and the electrical connecting means 72a, to the brush means 68 in the conventinonal manner. Insulating means 83 and 83a are provided for insulating the members 72 and 72a, respectively.

The commutator brush means 68 is operatively positioned relative to the commutator 60 within the brush holder 76 by the spring or similar resilient member 78 and is electrically insulated by insulating member 79. Double insulation for the brush means 68 is provided by back cap 22 which overlies the brush means 68 and forms the portion of the motor housing 14 extending thereabout.

The fan means 82 are positioned upon the forward end of the shaft 52; and the shaft 52 is operatively connected to the impact anvil 20 in conventional manner.

Impact wrench 10, furthermore, may be provided with an insulated reversing switch (not shown) for reversing the operation of the tool. This reversing switch could be of any suitable construction and could be associated with the back cap 22 such that the back cap 22 provides protecting insulation therefor.

The present invention comprises the provision of new and improved double insulating means for the motor 38, the electrical leads 30 and 36, and the trigger 28.

More specifically, the shaft 52 is provided with a layer or covering of functional insulation and a second layer or covering of protecting insulation and is, hence, doubly insulated. More specifically, as will be seen from FIG. 5, one of said layers or coverings of insulating material comprises a coating or covering of aluminum oxide 88 which is sprayed or otherwise positioned upon shaft 52. Materials other than aluminum oxide may be utilized for this layer of insulation, however, provided that the material employed has sufficiently high temperature and high strength characteristics and sufiicient dielectric strength to withstand the self-destructive forces arising as a result of the high temperatures and vibrations caused by operation of the impact wrench 10. A specific example of another such suitable material is mica glass. This layer of aluminum oxide 88 or other suitable material may be positioned on shaft 52 externally to armature winding 58 and commutator 60 only. Alternatively, if aluminum oxide or the like is employed, said insulating material may be provided on the shaft 52 throughout its length. The second of said layers of insulation comprises a paper sleeve or the like 84 positioned around said shaft 52 externally of its connection to the armature winding 58 and the commutator 60 such that a mechanical connection may be formed between the armature winding 58 and commutator 60 and the shaft 52.

The double insulating means provided for preventing electrical contact of the field coil 64 and the core 62 with the metallic motor housing 14 includes the layer of functional insulation which is formed by the insulating member 66 and the insulating coating formed upon the field coil 64. The protecting insulation for the coil 64 and the core 62 comprises a cylindrical housing or sleeve 86 which is constructed of a plastic or other suitable insulating material. The housing 86 is secured circumferentially of the coil 64 and the core 62 by the retaining means 88 which passes through the baffie insulator 94, the field core 62, the field insulator 96, and the housing 86 and into and is insulated by the bushing 90 which is of insulating material.

As will be seen from FIG. 5, the housing 86 includes a longitudinal slot 92 and may be formed integrally with the insulating sleeve 50 which affords double insulation for the insulated electrical leads 36 during their passage through the openings 40 and 42 in the handle 26 and the motor housing 14, respectively.

The forward end of the housing 86 is partially filled by a baffie insulator 24 which is constructed of insulating material and is provided for affording additional electrical insulation for the end turns of the insulated field coil 64 at the forward end of core 62. The insulator 94, in addition to providing protecting insulation for the field coil 64, serves as an air baffle to properly direct the air flow generated by the fan means 82. The insulator 94, further-more, may be formed integrally with the housing 86 or, alternatively, may be a member formed separately therefrom.

The rearward end of the housing 86 is partially closed by a field insulator 96 which is constructed of insulating material and provides protecting insulation to the windings of the field coil 64 upon the rear side of the motor 38. Field insulator 96, also, may be formed integrally with insulating housing 86 or may be a member separate therefrom.

Protecting insulation for the brush holder 76 and the reversing switch, should one be utilized, is, as was hereinbefore disclosed, supplied by the insulating back cap 22; and protecting insulation for the trigger 28 and the electrical leads 30 and 36 is supplied by the insulating handle 26.

The operation of the impact wrench 10- is believed to be apparent in view of the foregoing description.

From the foregoing, it will be seen that I have provided new and improved means for accomplishing all of the objects and the advantages of the invention.

I claim:

1. In an electrically powered hand tool, the combination comprising:

a housing;

a shaft rotatably mounted within said housing;

an armature carried by said shaft such that a portion of said shaft projects from said armature;

a commutator carried by said shaft and operatively connected to said armature;

commutator brush means disposed within said housing and operatively associated with said commutator;

a field structure including a field core and associated field coil disposed Within said housing and operatively connected to said armature; and

means upon said shaft for insulating said shaft;

said shaft insulating means comprising a coating of aluminum oxide provided on said shaft throughout the length of the portion of said shaft coextensive provide insulation for the end turns of said field coil; with said armature; and and a paper sleeve overlying the aluminum oxide on the means upon said shaft for insulating said shaft;

portion of said shaft coextensive with the end windsaid shaft insulating means comprising a coating of ings of the armature but external of the connection 5 aluminum oxide extending throughout the length of of the commutator with said shaft. the portion of said shaft coextensive with said arma- 2. In an electrically powered hand tool, the combinature; and

tion comprising: a paper sleeve overlying said aluminum oxide on a a housing including a barrel, a cap member carried by portion of said shaft coextensive with the end Windone end of said barrel, and a handle depending from ings of the armature but external of the connection said barrel; of the commutator with said shaft.

said cap member and said handle being constructed from electrically insulating material, said barrel being References Cited constructed from electrically conductive material; UNITED STATES PATENTS a shaft rotatably mounted within said barrel; 3,121,813 2/1964 Pratt an armature carried by said shaft such that portions of said shaft project from opposing ends of said 3242998 2/1966 Gub'bms Hog-5Q armature; FOREIGN PATENTS a commutator carried by said shaft and operatively 95 93 1 1953 Germany connected to said armature; 1,014,211 9/1952 Germany commutator brush means disposed within said housing 1 025 055 11/1956 Germany and operatively associated with said commutator; 1O66659 10/1959 Germany a field structure including a field core and associated 1110740 11/1959 Germany' field coil disposed Within said barrel and operatively 1130057 9/1961 German surrounding said armature;

470,690 2/1937 Great Britain.

a hollow sleeve of insulating material disposed W1th1n 725,842 3/1953 Great Britain.

said barrel intermediate said field structure and said barrel; t the opposing ends of said insulating sleeve being MILTON HIRSHFIELD Primary Exammer' partially closed by insulating filler means adapted to J. W. GIBBS, JR., Assistant Examiner. 

1. IN AN ELECTRICALLY POWERED HAND TOOL, THE COMBINATION COMPRISING: A HOUSING; A SHAFT ROTATABLY MOUNTED WITHIN SAID HOUSING: AN ARMATURE CARRIED BY SAID SHAFT SUCH THAT A PORTION OF SAID SHAFT PROJECTS FROM SAID ARMATURE; A COMMUTATOR CARRIED BY SAID SHAFT AND OPERATIVELY CONNECTED TO SAID ARMATURE; COMMUTATOR BRUSH MEANS DISPOSED WITHIN SAID HOUSING AND OPERATIVELY ASSOCIATED WITH SAID COMMUTATOR; A FIELD STRUCTURE INCLUDING A FIELD CORE AND ASSOCIATED FIELD COIL DISPOSED WITHIN SAID HOUSING AND OPERATIVELY CONNECTED TO SAID ARMATURE; AND MEANS UPON SAID SHAFT FOR INSULATING SAID SHAFT; SAID SHAFT INSULATING MEANS COMPRISING A COATING OF ALUMINUM OXIDE PROVIDED ON SAID SHAFT THROUGHOUT THE LENGTH OF THE PORTION OF SAID SHAFT COEXTENSIVE WITH SAID ARMATURE; AND A PAPER SLEEVE OVERLYING THE ALUMINUM OXIDE ON THE PORTION OF SAID SHAFT COEXTENSIVE WITH THE END WINDINGS OF THE ARMATURE BUT EXTERNAL OF THE CONNECTION OF THE COMMUTATOR WITH SAID SHAFT. 